Synced up llviewerobjectbackup with Cool VL Viewer

Benefits:
-Support for exporting Materials (Normal and Specular textures)
-Fixed support for Object Physics export
-Fixed support for Light Image export
-Switch to use of Boost unordered containers
-Checking for invalid perms on textures is now optimized by saving invalid ids to a container
-GravityMultiplier parameter is now Gravity because that just makes way more sense.
-We support export of legacy flag parameters again to be compatible with older viewers
-Code comments are now a little clearer
-We now wait a little if objects haven't loaded yet when we try to export them
-We no longer allow changing default texture ids via debug settings on opensim regions that support the export permission
-Bit of reordering to better diff with Cool VL Viewer, since it's essentially our only upstream.
-Removes dead code/commented codestuffs

Please view the diff without space changes, otherwise you'll lose your mind.

Merci Henri!